Process of flocculating aqueous suspensions with cationic starch ethers

ABSTRACT

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

United States Patent 3,842,005 PROCESS OF FLOCCULATING AQUEOUS SUSPEN-SIONS WITH CATIONIC STARCH ETHERS Kenneth B. Moser and Frank Verbanac,Decatur, Ill., assignors to A. E. Staley Manufacturing Company, Decatur,Ill.

No Drawing. Continuation-in-part of application Ser. No. 51,605, July 1,1970. This application Jan. 24, 1972, Ser. No. 220,386

Int. Cl. C02b 1/20; C02c 3/00; ROM 21 /01 US. Cl. 21047 Claims ABSTRACTOF THE DISCLOSURE BACKGROUND OF THE INVENTION This application is acontinuation-in-part of our application Ser. No. 51,605 filed July 1,1970, entitled Cationic Starch Ether F locculatz'ng Agents.

Much interest has recently been expressed in quaternary ammonium ethersof starch due to their cationic nature. A formal positive charge isretained by the quaternary ammonium starch ether at both alkaline andacid pH conditions. Gelatinized quaternary ammonium starch ethers havebeen used as fiocculating agents, or flocculants. It is generallybelieved that flocculation is due to the attraction between thepositively charged groups of the starch ether and the negatively chargedsuspended bodies which then form aggregates of suflicient particle sizeto settle from suspension.

In the past, only quaternary ammonium starch ethers having relativelylow degrees of substitution have been used as flocculants. The termdegree of substitution, or D.S., as used herein refers to the averagenumber of cationic substituent groups (derived from the etherifyingagent) that have become bonded to each recurring anhydroglucose unit ofthe starch molecule. Only the low D.S. quaternary ammonium starch etherswere used because it was generally thought that the high D.S. quaternaryammonium starch ethers would provide no additional fiocculating capacityrelative to the low D.S. ethers.

Prior patents actually teach away from the use of high D.S. starchethers as fiocculating agents. For example, US. Pat. 2,995,513, issuedAug. 8, 1961, to Paschall et al. states that the fiocculating capacityof gelantinized qua-ternary ammonium starch ethers increases with thedegree of substitution up to a level of 0.4-0.5 D.S. Beyond this D.S.level, Paschall et al. state that the fiocculating capacity levels ofiso that there is no advantage in using a quaternary ammonium starchether with a D.S. level greater than 0.5 (see Paschall et al. column 2,lines 19- 25). The highest D.S. starch ether prepared by Paschall et al.was one having a D.S. of 0.66 in Example 13, and this particular starchether was shown to be only about 75% as effective as a starch etherhaving a D.S. of 0.45 as described in Example 9 of Paschall et al. Basedon Paschall et al.s observation there was no suggestion that cationicstarch ethers having D.S. levels greater than 0.5

"ice

would be effective fiocculating agents. Higher D.S. quaternary ammoniumstarch ethers oifered no advantage over the low D.S. ethers in thoseapplications where they were tried. Because low D.S. starch ethers areless expensive to prepare, they have been used in preference to highD.S. starch ethers as fiocculating agents.

For certain applications, such as flocculation of dilute aqueous claysuspensions, the low D.S. quaternary ammonium starch ethers areinadequate, and until now synthetic coagulants have been used in thesesituations at a substantially greater cost. Another disadvantage ofthese synthetic coagulants is that they are generally not biodegradable.There is a definite commercial need for an effective fiocculating agentto replace synthetic coagulants and for many other applications. But,until now, high D.S. quaternary ammonium starch ethers were notconsidered because it was generally believed they were no better than,and in some cases less effective than, starch ethers with D.S. levels of0.4-0.5.

Contrary to the teaching to be gathered from the prior art, we have madethe surprising discovery that there are applications in which thefiocculating capacity of quaternary ammonium starch ethers substantiallyincreases as the D.S. of the starch ether increases above 0.7. This hasproved to be true with dilute aqueous clay suspensions. Although we donot want to be limited by theoretical considerations, one plausibletheory for the continued improvement in fiocculating capacity at D.S.levels of 0.7 and above is that as cationic charge density continues toincrease, the increased proximity of the charges on the starch moleculeenhance the capacity of the quaternary ammonium starch ether to attractthe negatively charged particles in suspension. When large sizedaggregates are formed by this interaction, the particles readily settlefrom suspension.

DETAILED DESCRIPTION OF THE INVENTION The present invention is primarilydirected to flocculation of materials suspended in aqueous systems bythe addition of a non-crosslinked, gelatinized quaternary ammoniumstarch ether with a D.S. of at least 0.7. These starch ethers can befreed from low molecular weight quaternary ammonium impurities andinorganic salts to provide suitable products for various particularapplications which require a purified flocculant.

The fiocculating agent of the present invention comprises a gelatinized,non-crosslinked cationic starch ether having a degree of substitution ofat least 0.7 and having the following structure:

wherein St is starch, X is an anion, and the substituents R R and R areselected from the group consisting of: 1) R R and R being selected fromthe group consisting of alkyl of up to 12 carbon atoms, cyclohexyl,phenyl and benzyl such that when the three are the same, none has morethan 6 carbon atoms and, when any substituent has more than 6 carbonatoms, the other two substituents are alkyl of up to 2 carbon atoms; and(2) R and R forming a heterocyclic ring with said nitrogen atom, theheterocyclic ring being selected from the group consisting ofmorpholinyl, pyrrolidyl and piperidyl, each having up to one alkyl ringsubstituent of not more than two carbon atoms, and R being a lower alkylof up to 4 carbon atoms. Of course, it is recognized that the activefiocculating species is the quarternary amonium cation.

The starch ethers preferred for use in the process of this invention maybe prepared as generally set forth in US. Pat. 3,346,563, issued Oct.10, 1967, to Shildneck et al. This patent, which along with the presentapplica-- tion is assigned to a common assignee, teaches the productionof low D.S. cationic starch ethers for use primarily in the papermakingindustry. These low D.S. starch ethers have been found to be entirelysatisfactory for papermaking applications and are, in fact, preferredover the high D.S. ethers which give inferior performance. This is yetanother reason why work has been concentrated on the low D.S. ethers tothe almost total exclusion of the high D.S. ethers.

The following equations show the steps of the process:

Equation (1) shows the reaction of tertiary amine, N(R R ,R with allylhalide, CH =CHCH X, to form an allyl quaternary ammonium halide,

The allyl quaternary ammonium halide should be ess. ntially free fromexcess allyl halide and allyl alcohol to avoid crosslinking of the finalstarch ether. crosslinkiig diminishes the flocculating capacity of theether.

The tertiary amine employed in the production of tle starch ethers isselected from the group consisting of: (1) tertiary amines Whose threesubstituents on the nitrogen atoms are selected from the groupconsisting of alkyl of up to 12 carbon atoms, cyclohexyl, phenyl andbenzyl such that when the three substituents are the same, none containsmore than 6 carbon atoms, and when any one substituent has more than sixcarbon atoms the other two are alkyl of up to two carbon atoms; and (2)heterocyclic tertiary amines, wherein the third substituent on thenitrogen of the ring is lower alkyl up to four carbon atoms, theheterocyclic ring being selected from the group consisting ofmorpholinyl, pyrrolidyl and piperidyl, each having not more than onealkyl ring substituent of up to two carbon atoms. The structural formulafor these tertiary amines is:

Rr-N-Rz it.

wherein R R and R are the substituents, as defined immediately above, Rand R being two substituents that can be part of a heterocyclic ringwith the nitrogen atom.

Trimethylamine (R R and R all being methyl) is the preferred tertiaryamine because of ready availability, low cost per equivalent weight,high reactivity with allyl halides to form the quaternary ammoniumsalts, and high solubility in water. The quaternization reaction ispreferably carried out in a water medium and the trimethyl quaternaryammonium etherifying reagents, being water soluble, are thereforepreferred. In addition, the starch ethers derived from these reagentsexhibit properties desirable for use as flocculating agents.

Other tertiary amines which may also be used in the reaction are asfollows:

triethylamine, triisopropylamine, tri-n-butylamine,N,N-dimethyldodecylamine, N,N-dimethylcyclohexylamine,N,N-dimethylbenzylamine, N-methylmorpholine, N-methylpiperidine,N-ethylpiperidine, N,N-dimethylaniline, N-methylpyrrolidine,

4 N,N-dimethyl-2-ethylhexylamine, N-methyl-2-methylmorpholine,N-methyl-Z-ethylmorpholine, N-methyl-Z-methylpiperidine,N-methyl-2-ethylpiperidine, N-methyl-Z-methylpyrrolidine, andN-methyl-Z-ethylpyrrolidine.

Of the three allyl halides-chloride, bromide and iodide-- allyl chlorideis preferred because of its lower cost per equivalent weight for thisreaction, even though it has the slowest reaction rate.

As shown in Equation (2), the allyl quaternary ammonium halide isreacted with a hypohalous acid, HOX, to yield the corersponding vicinalhalohydroxypropyl derivatives, CH OHCHX-CH N+(R R R )X*,

as well as a certain amount of the vicinal dihalopropyl derivative, CHX-CHXCH N+(R R R )X-. Both 2, 3-vicinal halohydroxypropyl quaternaryammonium halide isomers are useful in preparing the starch ethers of thepresent invention. It should be noted that the halide ion associatedwith the allyl quaternary ammonium halide need not be the same as thehalide ion associated with the hypohalous acid. That is, these two ionsare independently selected from the group consisting of halide ions.Hypochlorous acid is preferred over the other hypohalous acids inReaction (2) because of its greater selectivity to the desiredhalohydroxy derivative and lower cost per equivalent Weight.

At this stage in the process, vicinal halohydroxypropyl quaternaryammonium halide is present in aqueous solution along with the vicinaldihalopropyl derivative and some inorganic halide obtained byneutralizing the acidic reaction medium. The solution can beconcentrated by evaporation of water. After concentration, the bulk ofthis inorganic halide is removed by filtration; however, a small amountof the salt remains in solution. The efficiency of the starchetherification reaction increases as the concentration of the reactantsis increased, and therefore, highly concentrated reagents are preferred.The terms efficiency and etherification efficiency, as used herein,refer to a measure of the percentage of available starch etherifyingagent that actually becomes bonded to the starch.

The starch etherification itself, Reaction (3), is performed in thepresence of an alkaline catalyst. Generally, such alkaline catalystsinclude: (1) hydroxides, alcoholates and Weak-acid salts of the alkalimetals; (2) the oxides and hydroxides of calcium, barium, and strontium;and (3) quaternary ammonium bases. Specific compounds include sodiumhydroxide, potassium hydroxide, lithium hydroxide, calcium oxide,calcium hydroxide, barium hydroxide, strontium hydroxide,trimethylbenzyl ammonium hydroxide, sodium methylate, sodium aluminate,trisodium phosphate and sodium silicate. Sodium hydroxide is thepreferred alkaline catalyst because it is readily available and it isinexpensive.

The actual starch etherifying agent is vicinal epoxypropyl quaternaryammonium halide which can be obtained from the vicinal halohydroxypropylderivative by reaction with the alkaline compound described above. Thesalt by-product that results from this reaction need not be removed fromthe reaction system.

The di-halopropyl quaternary ammonium halide which is present as animpurity in the vicinal halohydroxypropyl derivative is destroyed byreaction with a stoichiometric quantity of the alkaline compounddescribed above. The di-halopropyl derivative is apparentlydehydrohalogenated. The halide salt that is a by-product of the reactionbetween the di-halopropyl derivative and the alkaline compound does notinterfere with the starch etherification reaction and need not beremoved from the reactinn system.

In the above reaction, it is important to provide sufiicient alkalinecompound to 1) catalyze the starch etherification, (2) convert thevicinal halohydroxypropyl derivative into the actual starch etherifyingagent (vicinal epoxypropyl quaternary ammonium halide), and (3) destroythe vicinal di-halopropyl quaternary ammonium halide.

Pure vicinal halohydroxypropyl quaternary ammonium halide or purevicinal epoxypropyl quaternary ammonium halide can be used to etherifythe starch instead of the relatively impure vicinal halohydroxypropylquaternary ammonium halide-vicinal di-halopropyl quaternary ammoniumhalide mixtures described above. The crystalline vicinalhalohydroxypropyl quaternary ammonium halide may be prepared by reactingepihalohydrin and tertiary amine hydrohalide. The crystallineepoxypropyl derivative can be prepared by reacting epihalohydrin andtertiary amine in a non-aqueous solvent, such as dimethoxyethane. Wheneither of these two halides is used to etherify starch, the amount ofalkaline compound needed for etherification should be adjustedaccordingly. That is, if pure vicinal halohydroxypropyl quaternaryammonium halide is used, suflicient alkaline compound must be presentduring starch etherification to (1) catalyze the etherification, and (2)convert the vicinal halohydroxypropyl quaternary ammonium halide to theactual etherifying reagent, vicinal epoxypropyl quaternary ammoniumhalide. However, if the pure vicinal epoxypropyl derivative is used,only the catalytic amount of alkaline compound is required.

The starch ethers of the present invention may be produced in thefollowing manner. An aqueous starch slurry containing the requiredamount of alkaline compound to catalyze the etherification reaction isprepared. The etherifying agent or its precursor (vincinal epoxypropylquaternary ammonium halide or vicinal halohydroxypropyl quaternaryammonium halide) is combined with any remainder of the necessaryalkaline compound in a separate vessel. Less alkaline compound than isneeded to produce and/or purify the etherifying agent may be added tothis separate vessel in order to avoid degradation of the etherifyingagent. (The remaining alkaline compound is added directly to the starchslurry.) At this point, the temperature within the separate vesselshould be maintained below about 90 F. to avoid undesirable sidereactions.

The starch slurry is then heated to about 120 F. and, for best results,about to 20% of the etherifying reagent is added to the slurry. Thestarch slurry is then heated to its pasting temperature and theremainder of the etherifying agent is slowly added to the starchmixture. Alternately, to simplify the procedure, the alkaline compoundand the etherifying agent (or its precursor) can be simultaneously addeddirectly to the starch slurry, which is then pasted. Some etherificationmay occur before the starch is gelatinized. The starch mixture ismaintained at or above its pasting temperature for about 1 to 20 hoursto allow the etherification to occur.

If desired the halide ion of the starch ethers can be replaced withanother anion, by means of ion exchange or other well known methods.Suitable anions include nitrate ion, acetate ion, sulfate ion, phosphateion and the like.

For most flocculating applications, the complete reaction mass can beused without purification of any kind. However, in certain flocculationservices, purification of the reaction mass may be necessary.

The starch ethers of the invention may be purified by dialysis of thecrude starch ether containing the reaction mixture against distilledwater to remove or separate the low molecular weight quaternary ammoniumby-products and inorganic salts from the starch ether. Alternately, anultrafiltration cell having a selectively permeable membrane can be usedto retain the cationic starch ether while allowing the low molecularweight organic and inorganic impurities to pass through in the aqueousfiltrate.

The starch ethers can also be purified through ion exchange. To removethe quaternary ammonium by-products, the reaction mixture is broughtinto contact with a sulfonic acid type cation exchange resin (in thesodium form). After this purification, the cationic starch ether remainsin an aqueous solution containing inorganic impurities. Separation ofthe inorganic salts, plus the quaternary ammonium by-products from thestarch ethers can be accomplished by treating the reaction mixture witha mixture of sulfonic acid cation exchange resin (in the acid form) anda weakly basic polyamine anion exchange resin (in hydroxyl form). Thisproduces an aqueous solution of the quaternary ammonium starch etherswhich is essentially free of low molecular weight ionic impurities.

The above purification techniques provide starch ethers which can betailor made for a particular use. Only those specific impurities areremoved which are objectionable to the intended use, thereby avoidingexcess purification costs. The D.S. level of the starch ether producedcan also be controlled to provide the optimum D.S. for the particularuse contemplated.

Different types of starch will give starch ethers of differentproperties. This invention is applicable to all types of starch andstarch fractions, including dextrins, waxy, and high-amylose varietiesof starch. The starch may be derived from the root (e.g., potato,tapioca), the stem (e.g., sago), or the seed (e.g., cereals, corn, wheator rice) of the vegetable plant. The starch may have been modifiedbeforehand, in paste or granule form, with acids, enzymes, or heat.Also, the starch or dextrin may have been partially derivatizedbeforehand as, for example, by reaction with alkyl halides to form alkylstarch ethers, or by reaction with alkylene oxides to form thehydroxyalkyl ethers of starch. The important requirement is that thestarch have reactive hydroxyl groups remaining after such modification.Other compounds, such as polyvinyl alcohol, and other synthetic polymerscontaining free hydroxyl groups, can also be used in the method of thepresent invention.

The types of starch used alfects the character of the fiocculantproduced. For example, amylose will produce straight chain flocculants.Amylopectin, by contrast, produces branched chain flocculants. Mixedstraight and branched chain flocculants are produced when dent cornstarch is used. Potato starch will normally produce flocculants withvery low levels of anionic character (i.e., the naturally occurringphosphate groups). Low molecular weight flocculants can be obtained byusing hydrolyzed starch. Other substituents added to the starch moleculevia well known modification reactions also influence the character ofthe resulting flocculant.

The high D.S. cationic starch ethers of the present invention aresuitable for a wide variety of uses which include clarifying turbidwater, iron oxide slurries, kaolin slurries, predispersed kaolinslurries (which are more difficult to flocculate than raw kaolinslurries), taconite slurries, coal slurries, silica slurries, sewagewaste waters, calcium carbonate slurries, titanium dioxide slurries,carbon slurries, and animal slaughterhouse waste waters. Substantiallyall aqueous suspensions in which the solid particles carry a negativecharge can be clarified by employing the cationic starch ethers of thepresent invention.

Systems in which the flocculating capacity of the starch ethers of theinvention increase substantially beyond a D.S. level of 0.7 includekaolinite clay slurries, predispered kaolin clay slurries, coal washwater, calcium carbonate slurries, titanium dioxide slurries, sliciasuspensions, turbid water, iron oxide slurries, taconite slurries andcarbon slurries. As mentioned above, such high D.S. level systems werenot used before applicants invention because it was generally believedthat no improved flocculating capacity would be realized at D.S. above0.5.

The cationic starch flocculants of the invention were tested withaqueous clay suspensions by preparing an aqueous kaolinite claysuspension, with clay concentration of 50 ppm. by weight. One liter ofthis suspension was placed in a larger container equipped with amultiple speed laboratory stirrer and mixed at 100 r.p.m. The flocculantsolution (100 mg. of reaction mixture diluted in one liter of water andthoroughly mixed) was pipetted into the kaolinite clay suspension Whilestirring at 100 r.p.m. and stirring was continued for 20 minutes. Thestirring speed was then decreased to r.p.m. for an additional minutesafter which the stirrer was stopped. Unless otherwise specificallynoted, the turbidity measurements were made on the clarified suspensionthat existed 5 minutes after the mechanical stirring was stopped. Theoptimum dose of flocculant was determined by running several tests atvarious flocculant concentrations. The optimum dose is defined as thelowest dosage that gives a finished water of good clarity.

Our invention is illustrated, but not limited bythe following examples.

EXAMPLE 1 A slurry of 11.37 parts dry substance hydrolyzed corn starch,having a 5 gram alkali fluidity of 70 cc., and 37.00 parts of water wasprepared. Localized pasting of the starch was avoided by adding 2.18parts of a 15 wt. percent aqueoussodium hydroxide solution to theslurry. Unless otherwise specified, weight parts are used throughout theexamples.

In a separate tank, equipped with cooling coils, 11.20 parts of a 50 wt.percent aqueous sodium hydroxide solution was slowly added to 33.43parts of a reagent with a typical composition of:

74 wt. percent chlorohydroxypropyltrimethyl ammonium chloride 6 wt.percent dichloropropyltrimethylammonium chloride 2 Wt. percent sodiumchloride 18 wt. percent water This reagent can be produced by firstreacting allyl chloride with trimethylamine. The product is then reactedwith hypochlorous acid. These two reactions are discussed in much detailin US. Pat. 3,346,563. The production of the reagent is completed byevaporation of a portion of the aqueous reaction medium, and anyby-product salt is removed, for example by filtering or centrifuging.

Etficient stirring and cooling was provided to rapidly disperse thesodium hydroxide throughout the reagent.

'The reagent mixture was maintained below 60 F. during and after theaddition of alkali. At this point some sodium chloride precipitated fromthe mixture; however, this salt was kept in suspension by stirring andno attempt was made to remove it.

The starch slurry was slowly heated. When the temperature of the slurryreached 80 F., 6.00 parts of the reagent mixture was added to theslurry. The temperature of the slurry was slowly increased to 160 R,which was suificient to paste the starch. As the starch started topaste, the remainder of the reagent mixture was slowly added. Thisgradual addition of the reagent mixture occurred over about a one-hourperiod. The tank which contained the reagent mixture was rinsed with2.64 parts of water, which was then added to the starch paste. Thetemperature of the starch paste was maintained at 160 F. for 5 hoursafter all the reagent mixture had been added. The starch pasted was asthen cooled to 100 F. and 32 wt. percent aqueous hydrochloric acid wasused to neutralize the mixture to a ph of 6.5, :0.5. If necessary, 15wt. percent aqueous sodium hydroxide can be used to back titrate.

The resulting gelatinized quaternary ammonium starch ether wassubstantially free of crosslinking and had a D.S. of 1.02.

This starch ether was tested in the laboratory in clay flocculationservice. The measure of performance was Jackson Turbidity Units(J.T.U.). Following the general procedure outlined previously, theturbidity of a clay suspension with 50 p.p.m. clay was reduced fromapproximately 82 J.T.U. to 14.0 J.T.U. and 3.8 J.T.U. by the addition of0.11 and 0.18 p.p.m. of the starch ether, respectively. Throughout theexamples, starch ether concentrations are based on dry substance starchether.

EXAMPLE 2 In this example, pure vicinal halohydroxypropyl quaternaryammonium halide was used to produce flocculants for an aqueous claysuspension.

A slurry of 36.4 parts of a hydrolyzed corn starch, having a 5 gramalkali fluidity of 70 cc., 128.0 parts of water, and 1.6 parts of a 50wt. percent aqueous sodium hydroxide solution was prepared and heated to122 F. In a separate holding tank, a solution of 80.0 parts of vicinalchlorohydroxypropyltrimethylammonium chloride, 38.0 parts of water and34.0 parts of 50 wt. percent aqueous sodium hydroxide was made up sothat the temperature was kept below about 86 F. One half of the vicinalchlorohydroxypropyltrimethylammonium chloride solution was added to thestarch mixture. The temperature of the starch mixture was increased toabout F. and the other half of the reagent solution was added dropwiseover a one hour period. The tank in which the reagent solution wasprepared was rinsed with 10.0 parts of water which was then added to thestarch paste. The paste was maintained at about 160 F. for 5 additionalhours, after which the mixture was cooled and neutralized to a pH of 6.7with concentrated hydrochloric acid.

The resulting non-crosslinked gelatinized cationic quaternary ammoniumstarch ether had a D.S. of 1.02, and reduced the turbidity of an aqueousclay suspension with 50 p.p.m. clay from 77 J .T.U. to 7.3 J.T.U. and4.0 J.T.U. by the addition of 0.10 and 0.17 p.p.m. of the starch ether,respectively.

EXAMPLE 3 Example 2 was repeated except that the starch used was anunmodified corn starch. The resulting starch ether had a D.S. of 0.93.This starch ether reduced the turbidity of a clay suspension with 50p.p.m. clay from 77 J.T.U. to 6.1 J.T.U. and 4.9 J.T.U. by the additionof 0.16 and 0.32 p.p.m. of the starch ether, respectively.

EXAMPLE 4 EXAMPLES 5-6 Examples 2 and 4 were repeated except that theamount of water used to slurry the starch was halved. Example 5corresponds to Example 2 and Example 6 to Example 4. Each of theresulting starch ethers was tested in clay flocculation service andfound to be satisfactory fiocculants. The table below gives a comparisonof the D.S. of these ethers with that of the ethers prepared in Examples2 and 4.

TABLE Example: Starch ether, D.S. 2 1.02

The above table supports the conclusion that etherification efliciencyis increased as the water concentration is decreased.

9 EXAMPLES 7-10 The following examples illustrate the effect of starchether D.S. on clay flocculating capacity. A slurry composed of 32 partsof a hydrolyzed corn starch with a gram alkaline fluidity of 90 cc. and89 parts of water was prepared. The slurry was pasted by stirring andheating to about 200 F. followed by cooling to about 113 F. Stirring wascontinued while 3.2 parts of 50 wt. percent aqueous sodium hydroxide (acatalytic amount) was added. The desired amount of the actualetherifying agent, 2,3-epoxypropyltrimethylammonium chloride, was addedand the reaction was allowed to continue overnight. The amount ofetherifying agent added depends on the D.S. desired for the resultingstarch ether. After cooling, the pH of the starch mixture was adjustedto 65:0.2 with hydrochloric acid.

The resulting gelatinized quaternary ammonium starch ethers aresubstantially free of cross-linking. The compilation below shows how theclay flocculating capacity of these starch ethers is dependent on theD.S. of the starch ether.

TABLE Wt. etherifying Charge Optimum dose agent used/wt. density forclay flocdry substance of starch culation, p.p.m. Example starch etherstarch ether The term ClargeDDsensity as used herein is defined asCharge Density=- 162 D.S. (MWs-l) Where:

C is the number of cationic charges per substituent group.*

D.S. is the degree of substitution, as defined previously.

162 is the molecular weight of a recurring anhydroglucose unit, and

MW is the molecular weight of the substituent group. These figuresclearly illustrate that the clay flocculating capacity of these starchethers continues to increase as the D.S. increases beyond 0.40 and 0.63up to at least 0.82.

EXAMPLES 11-15 These examples illustrate that as the starch ether chargedensity increases (an inherent result of an increase in D.S.), thenumber of cationic charges needed for a given flocculating applicationdecreases. The starch ethers were prepared in a manner similar to thatof Example 1.

The flocculating capacity of these starch ethers was tested using anaqueous slurry of 320 p.p.m. of a kaolin coating clay predispersed withapproximately 0.30% by weight of (based on clay) tetrasodiumpyrophosphate. The turbidity of this slurry initially was about 530J.T.U. The amount of starch ether necessary to clarify this claysuspension to 40 I.T.U. was determined and this value was translatedinto number of cationic charges necessary to flocculate one ton ofclay-from suspension. The results These results indicate that as thecationic charge density of starch ethers increases, the flocculatingcapacity of each individual charge increases. Apparently, two singlecationic *Substituent group refers to that part of the etherifying agentthat becomes bonded to the starch molecule.

charges in close proximity act to some extent as a single double chargeand this effect increases as the single cationic charges are broughtcloser together (as the charge density increases). These examplesclearly demonstrate the superior flocculating capacity of the high D.S.(greater than 0.7) ethers of the present invention as compared to theethers described in U.S. Pat. 2,995,513, particularly in Example 16.

EXAMPLES 16-18 The following examples indicate that the starch ethersemployed in this invention can be purified by various means withoutlosing any substantial part of their flocculating capacity.

The ethers used in these examples were prepared in a manner similar tothose used in Example 1. However, once the etherification reaction wascompleted, the ethers were freed of various contaminants by threepurification techniquesdialysis, ultrafiltration and ion exchange.

The ether treated by the dialysis technique (against distilled waterusing regenerated cellulose tubing having an average pore radius of 24angstroms) was freed low molecular weight quaternary ammoniumimpurities, such as unreacted etherifying agent, and inorganic salts.Ultra filtration (using a membrane through which molecules having amolecular weight less than about 100,000 are able to pass) also removedlow molecular weight impurities from the starch ether. By treating 30parts of the starch etherification reaction mixture with parts of asulfonic acid cation exchange resin in acid from (Rohm & Haas IR-Hresin) and 100 parts of a weakly basic polyamine anion exchange resin inhydroxyl form (Rohm & Haas IR45 resin), the starch ether is essentiallyfreed of quaternary ammonium impurities and inorganic salts.

These purified quaternary ammonium starch ethers were tested in clayflocculation service. The results of these tests are summarized below:

Clay flocculation test J.T.U., p.p.m. starch ther Method of Examplepurification D S 0 08 0.10

Unpurified ether 1. 02 12 J.T.U 5 J.T.U. 16 Dialysis 1.04 13 J.T.U 5J.I.U. 17 Ultrafiltration. 1.02 13 .T.T.U 5 J.T.U. l8 Ion exchange 1.0214 I.T.U 5 J.T.U.

The above compilation indicates that the purified starch ethers are onlyvery slightly reduced (it reduced at all) in their flocculatingcapacities compared to the unpurified ether.

In certain applications, such as production of potable water, it isnecessary to use a purified flocculant, and the purified quaternaryammonium starch ethers tested proved to be very effective flocculatingagents.

EXAMPLE 19 Sludge conditioning in vacuum filtration system Theflocculating agent of the invention was used successfully in a largemunicipal sewage waste treatment plant which employed a vacuumfiltration system incorporating vacuum coil-type filters, presentlymanufactured by Komline-Sanderson Engineering Corp. of Peapack, NJ. Inthese runs, the flocculating agent of the invention was substituted fora more expensive synthetic cationic flocculating agent which had beenused in the plant for about Inall the above tests upon which the abovecomparisons were based, the waste efiluents were conditioned with about35% by weight of the same anionic polymer, based on the dry weight ofthe particular flocculating agent, prior to the addition of theflocculating agent. The respective flocculating agents were added to thewaste liquor just prior to the point in the system where the wasteliquor enters the sludge filters (described above). The comparisons forthe synthetic flocculating agent were based on a series of about seveneight hour filtering runs, three of which were made end-to-end withapplicants three eight hour test runs. The annual cost saving by usingapplicants product has been calculated for this particular plant to beabout $10,000, based on present prices as set forth above.

It is also believed at present that the flocculating agent of theinvention leaves behind a more natural solids residue because of thestarch component, and this fact should make more feasible the ultimatedisposal of the wastes through land fill, combustion-incineration,fertilizer manufacture, or other similar means.

EXAMPLE 20 Paper pulp mill-process water purification Applicantsflocculating agent has also been used successfully in paper pulp millsin the recovery of chemicals from alkaline cooking liquors, referred toas the White and green liquors and in the mud Washers. In the typicalpulp recovery system, strong black liquor containing sodium compounds,and organic chemicals is converted to green liquor by first burning itin a recovery furnace and by adding make-up chemicals, such as sodiumsulfate, and placing the mixture in a dissolving tank. The flocculatingagent is added to the green liquor as it flows from the dissolving tankinto the green liquor clarifier, and is used to remove carbon and otherinsoluble particles suspended in the green liquor. Applicantsflocculating or settling effect on green liquor was observed andcompared to a control run with the following results:

TABLE.PULP MILL GREEN LIQUO R-SETTLING EFFECT OBSERVED Applicantflocculating agent p.p.m.) settling Time,

efiect Control (no flocculating minutes agent) settling effect It can beseen from the above data that applicants flocculating agent has verydefinite and visible settling efiects in the pulp liquor processing. Inaddition to using the new flocculating agent of this invention at thispoint in the pulp liquor processing, it can also be added to the whiteliquor which is derived from the clarified green liquor. This secondaddition insures that all of the solid calcium carbonate is completelyremoved from the recovered chemicals prior to recycling them to thepaper pulp digester. Careful and judicious use of pulp processing watersand chemicals is especially important in those states where strictenforcement of clean water laws is being carried out. In addition, itmakes good sense in production economies to recycle as much of the pulpdigester chemicals as possible, besides the good sense associated withimproving the public image of pulp processors.

EXAMPLE 21 Clarification of coal mining wash waters The flocculatingagent of the subject invention was compared to Synthetic A, acommercially accepted synthetic cationic polymer, which is presentlyused in clarifying coal processing wash Waters which contain substantiallevels of suspended clay. The results observed were as set forth below:

TABLE.SETTLING EFFECT OBSERVED 1 p.p.m. anionic} The Synthetic A is acommercial available flocculating agent which has been used for severalyears by coal mining companies in wash water processing, and itsperformance has been accepted by them as standard. In reading Table II,it can be seen that applicants flocculating agent outperformed thecommercially accepted flocculating agent, Synthetic A, by more thanabout on settling level comparison. It took one minute, 25 seconds toaccomplish the same level of settling effect with Synthetic A as wasobserved after only 57 seconds with applicants flocculating agent, allother conditions being the same. In a coal mining wash water purifyingsystem, this represents a substantial cost saving in capital investmentfor wash water purification. In addition, the present cost per ton ofthe flocculating agent of the invention is about $240 less than the costper ton for Synthetic A. Disposal problems are expected to be less forapplicants flocculating agent residues, for the same reasons asmentioned above in Example 19.

Since many embodiments may be made of this invention and since manychanges may be made in the em bodiments thereof, the following is to beinterpreted as illustrative only and the invention is defined by theclaims appended hereafter.

What is claimed is:

1. The process of flocculating material from an aqueous suspensioncomprising treating said aqueous suspension with a gelatinized,non-crosslinked quaternary ammonium starch ether having a D5. of atleast 0.7 and having a structure selected from the group consisting of:

wherein St is starch, X- is an anion, and the substituents R R and R areselected from the group consisting of alkyl of up to 12 carbon atoms,such that when the three substituents are the same, none has more than 6carbon atoms, and when any substituent has more than 6 carbon atoms, theother two substituents are alkyl of up to 2 carbon atoms; and R is alower alkyl of up to 4 carbon atoms, said starch ether having a chargedensity of about 2.61 X 10* and having at least 200 anhydroglucose unitsper starch ether molecule, said starch ether being substantially free ofresidual crosslinking agents including polyfunctional starch etherifyingagents and dihalo organic crosslinker reaction by-products and about3.35 lbs. said starch ether being capable of flocculating about 1 ton ofclay from an aqueous suspension of 320 p.p.m.

of a kaolin coating clay predispersed with approximately I 0.30% byweight of tetrasodium pyrophosphate, based on the weight of clay, saidaqueous suspension having an initial turbidity of about 530 J.T.U., to afinal turbidity of less than about 40 I.T.U.

2. The process of claim 1, wherein X is a chloride ion.

3. The process of claim 1, wherein R R and R are methyl groups.

4. The process of claim 1, wherein X- is a chloride ion and R R and Rare methyl groups.

5. The process of claim 4 wherein said starch ether is capable offlocculating said aqueous suspension when treated with about 2.31 to3.35 pounds of said starch ether per ton of suspended solids to beflocculated, said starch ether being derived from the alkaline reactionof vicinal epoxypropyl quaternary ammonium chloride which generatedihalopropyl by-products and having substantially all of saiddihalopropyl by-products transformed into salts by the excess alkalipresent in the reaction mixture, and in which the aqueous suspension isslaughterhouse wastes.

6. The process of claim 5, wherein said aqueous suspension compriseskaolin clay and tetrasodium pyrophosphate.

7. The process of claim 1, in which the aqueous suspension is a sewagewaste liquor, and including the steps of first conditioning the sewagewaste liquor by adding about 35% by weight of a synthetic anionicpolymer, based on the dry weight of said quaternary ammonium starchether.

8. The process of claim 1, in which the aqueous suspension is the spentliquor resulting from a pulp mill digester system, and the flocculatingagent is added selectively to clarify the green liquor, the whiteliquor, and to aid operation of the "mud washers.

9. The process of claim 1, in which the aqueous suspension is aclay-rich aqueous suspension of coal mining 14 wash water, and includingthe step of adding about 1 p.p.m. anionic material to the wash waterprior to the addition of said quaternary ammonium starch ether.

References Cited UNITED STATES PATENTS 2,995,513 8/1961 Paschall et a1.260-233.3 R 2,975,124 3/1961 Caldwell et al. 2l054 3,259,570 7/1966Priesing et al. 2l053 3,479,282 11/1969 Chamot et a1. 210-54 3,001,9339/1961 Malinowski 2l054 3,453,257 7/1969 Parmerter et al. 210-54XFOREIGN PATENTS 715,566 8/1965 Canada 260-233.? R

THOMAS G. WYSE, Primary Examiner US. Cl. X.R.

Column Column Column Column Column Column Column Column Column ColumnColumn Column Patent No.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

igned and sealed this 18th day of March 1975 (SEAL) Attest:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Inventor) KennethB. Moser and Frank ve b Dated 31; for 12; for 13; for 14; for 17; for15; for 64; for 66; for

Example 7; for "0. 77" read ---1.125--- Example 14; for "2.32 x 10 read---2.32 x 10 10, line 29; for "from" read ----form--- 10, line 40; for"ther" read ---Ether--- RUTH C. MASON Attesting Officer "1970, entitled"read ---l970, now abandoned, entitled-- "+CH ca" read ---+CH ca "C CH Cread ---CH CH C "X 0X" rt ad -X BOX-"- 2 H2 X'MOH" read ---X' MOH--"corersponding" read ---corresponding-- "pasted was as then" read---paste was then--- "ph" read ---pH--- c. MARSHALL DANN Commissioner ofPatents and Trademarks ORM PO-OSO (10-69)

1. THE PROCESS OF FLOCCULATING MATERIAL FROM AN AQUEOUS SUSPENSIONCOMPRISING TREATING SAID AQUEOUS SUSPENSION WITH A GELATINIZED,NON-CROSSLINKED QUATERNARY AMMONIUM STARCH ETHER HAVING A D.S. OF ATLEAST 0.7 AND HAVING A STRUCTURE SELECTED FROM THE GROUP CONSISTING OF: